1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic art such as a copying apparatus or a printer and to a cartridge removably mountable on this apparatus.
2. Related Background Art
In an image forming apparatus using an electrophotographic image forming process, there has heretofore been adopted a process cartridge system in which an electrophotographic photosensitive member and process means acting on the electrophotographic photosensitive member are integrally made into a cartridge which is removably mountable on an image forming apparatus body. According to this process cartridge system, the maintenance of the apparatus can be done by a user himself without resorting to a serviceman and therefore, operability could be markedly improved. So, this process cartridge system is widely used in image forming apparatuses.
Now, in an image forming apparatus using the aforedescribed cartridge system, to develop an electrostatic latent image formed on a photosensitive drum with a toner caused to adhere thereto, it is necessary for the toner to have a moderate charge (hereinafter referred to as the "tribo"). In the case of a developing device shown, for example, in FIG. 14 of the accompanying drawings, a toner 5 supplied onto a developing roller 7 (developer carrying member) is frictionally contacted by a developing blade 6 (developer regulating member) adhesively secured to a metal plate 6a when the developing roller 7 is rotated in the direction of arrow. Thereby, the toner 5 may be frictionally charged.
However, in a state shortly after the cartridge has begun to be used, i.e., the initial state, the toner 5 in the developing device 4 is scarcely charged. The charged toner 5 remaining on the developing sleeve 7 during development with the image forming operation repeated is collected into the developing device 4 and is agitated by an agitating bar 8 and is circulated in the developing device 4, whereby the tribo of the toner 5 in the developing device 4 gradually becomes higher.
Therefore, in the initial state of use of the cartridge, the tribo of the toner 5 on the developing sleeve 7 is low and a sufficient quantity of toner 5 does not adhere to the photosensitive drum 1. Thus, the density of a printed image has been reduced and a line width constituting characters, figures, etc. has become thin, and by the cartridge being used to some extent, the line width and the density of the image have sometimes been recovered.